In recent years, adverse influences of asbestos (fibrous silicate, also called Ishiwata in Japanese) on human bodies have become a problem. Specifically, companies announced that many people engaged in production of asbestos or in businesses handling asbestos in the past were suffering from health hazards such as lung cancer or mesothelioma. It was also reported that persons who inhaled asbestos dust have a risk of health problems such as pulmonary asbestosis, lung cancer, and malignant mesothelioma.
Pulmonary asbestosis is one kind of pulmonary fibrosis (pneumoconiosis) which is a disease making lungs fibrous. Although there are many causes, such as other mineral dust, for such fibrous lungs, pulmonary fibrosis caused by exposure to asbestos is especially referred to as pulmonary asbestosis, thereby being distinguished from the others. It is believed that asbestos fibers cause lung cancer mainly by physical stimulus caused by asbestos fibers taken in lung alveoli. The degree of carcinogenicity is varied among different kinds of asbestos, while diameter and length of asbestos also affect how carcinogenic the asbestos is. Malignant mesothelioma is a malignant tumor developed, for example, in pleura surrounding lungs and in peritoneum surrounding organs such as liver and stomach.
Asbestos encompasses chrysotile (white asbestos), crocidolite (blue asbestos), amosite (brown asbestos), anthophylite, toremolite, and actinolite. As for usage of asbestos, 90 percent or more is for building materials, and remaining 10 percent is industrial materials such as sealing materials for chemical plant facilities, friction materials, and the like. Although production etc. of building materials, friction materials, and adhesives made of asbestos has been prohibited since Oct. 1, 2004, there still remains asbestos in many buildings because asbestos had been used in large amounts in the past.
One example of a method for detecting asbestos is as follows. In detection of asbestos in an atmosphere, the atmosphere is sucked by a pump through a filter for collecting asbestos, and the filter is made colorless (transparent) with the use of acetone or the like and is then observed with the use of a phase-contrast microscope to measure a total fiber concentration in the atmosphere. In a case where the total fiber concentration is 1 or more fibers/L, it is determined with the use of an electron microscope whether fibers found by the observation by the phase-contrast microscope are actually asbestos or not (see Non-Patent Literature 1).
However, since observation using a phase-contrast microscope requires good skill and a considerable length of time, it is difficult to simultaneously carry out many observation processes. Moreover, since an electron microscope is a very expensive machine, it is not easy for everyone to conduct electron microscopic observation. Furthermore, determination using an electron microscope requires not only complicated sample pretreatment etc., but also a lot of time and patience because fibers observed by a phase-contrast microscope need be analyzed by an energy dispersive X-ray analyzer.
For these reasons, the conventional method using a phase-contrast microscope and an electron microscope (hereinafter referred to as “phase-contrast microscope/electron microscope method”) cannot speedily detect asbestos, and is therefore inapt for detecting an asbestos risk at a demolition work site where speedy detection is required. At a demolition work site, demolition is finished within two or three days at the earliest. Therefore, there are quite a few cases where asbestos has been already scattered around before an inspection result is obtained. Since asbestos generation sources in Japan are shifting from factories to demolition work sites, whose location change in a short time, there is an urgent need to develop a method for speedily detecting asbestos.
By the way, the inventors of the present invention independently discovered a protein which specifically binds to asbestos (referred to as “asbestos-binding protein”), and advocates an asbestos bioassay system using this protein (referred to as “bio-fluorescence method”) (see, for example, Patent Literature 1). The bio-fluorescence method is a method for detecting asbestos under a fluorescence microscope with the use of a bioprobe prepared by modifying the asbestos-binding protein with a fluorescent substance. The bio-fluorescence method makes it possible to detect, with good sensitivity, even finer asbestos fibers which are hard to observe under a phase-contrast microscope. Specifically, it is found that the bio-fluorescence method makes it possible to detect even fine chrysotile single fiber whose width (diameter) is 30 nanometers. Moreover, the bio-fluorescence method makes it possible to find out both physical properties and shapes of asbestos fibers. For these reasons, the bio-fluorescence method has been attracting attention as an efficient, easy and accurate asbestos detecting method.
Moreover, the inventors of the present invention reported that a DksA protein derived from Escherichia coli strongly binds to especially chrysotile (white asbestos) among a variety of asbestos (Non-Patent Literature 2).
Furthermore, the inventors of the present invention disclosed a screening method for an asbestos-binding protein and a method for detecting asbestos contained in a variety of samples by the bio-fluorescence method with the use of an asbestos-binding protein obtained by the screening method (Patent Literature 2).